1. Field of the Invention
The present invention relates to an apparatus for manufacturing semiconductor devices, and, in particular, to a vapor growth apparatus wherein a semiconductor crystal is grown by using an organometallic compound as a feed gas.
2. Description of the Related Art
Recently, apparatuses used in performing organometallic vapor growth methods have remarkably developed because of their simple structure and easy operation. The organometallic vapor growth methods are performed as shown in FIGS. 1A and 1B. Support or susceptor 2 made of carbon is disposed within reaction tube 1. Semiconductor wafer 3 is mounted on susceptor 2. A feed gas is introduced into reaction tube 1 through inlet 4. Wafer 3 is heated up to about 800.degree. C. by frequency coil 5 arranged outside of reaction tube 1, thereby to grow a semiconductor crystal on wafer 3. In this case, by changing the compositions of the feed gas, a plurality of different-kind semiconductor crystal layers are formed on wafer 3.
In this type of organometallic vapor growth method, it is necessary that the thickness of each crystal layer be uniform over the entire surface of wafer 3, in order to obtain an excellent yield.
According to conventional method of keeping uniformity in thickness of the crystal layer in the direction of the flow of feed gas, wafer-supporting face 40 of susceptor 2 is inclined so that a gas flow path becomes thinner toward the downstream side, as shown in FIG. 1B. By this method, the gas component consumed for crystal growth on the upstream side of wafer 3 is compensated on the downstream side due to increase of flow speed. Thus, the uniformity in thickness of the crystal layer can be maintained.
In a direction perpendicular to the flow of feed gas, the flow speed of the feed gas reaches a maximum value at the central area of reaction tube 1, and becomes zero in the vicinity of the inner wall of reaction tube 1 owing to the viscosity resistance. In other words, even if the concentration of the gas component to be consumed by crystal growth is constant, the flow speed of feed gas varies over the cross section of reaction tube 1; consequently, the thickness of the crystal layer in the direction perpendicular to the flow of the feed gas is large in the central area of wafer 3 and small in the peripheral area of wafer 3.
In order to solve this problem, for example, the size of reaction tube 1 may be increased, and wafer 3 may be located in a region where a variation in flow speed is small. Alternatively, wafer 3 may be rotated by mechanical means. In the former method, when the size of the apparatus becomes large, a convection eddy current is easily caused. In order to prevent the occurrence of the convection eddy current, it is necessary to increase the flow rate of feed gas, resulting in a rise in manufacturing cost. On the other hand, the latter method wherein wafer 3 is rotated is a surer method, in fact. However, it is difficult to design a rotation mechanism bearing at a high temperature of about 1,000.degree. C., and a special material must be used as a material constituting such a rotation mechanism. In addition, there are problems wherein solid material is precipitated on a rotational part of the rotation mechanism or the maintenance of the rotation mechanism is troublesome, compared to the conventional apparatus. Thus, the latter method is also disadvantageous.